Method of synthesizing an organophosphorus compound

ABSTRACT

A compound of formula ##STR1## where R 1  and R 2  are independently a C 1  -C 10  aliphatic radical, or R 1  is a C 1  -C 10  aliphatic radical and R 2  is a C 6  -C 10  aromatic radical, and R 3  is a C 1  -C 8  aliphatic radical, a C 3  -C 8  cycloaliphatic radical, a C 6  -C 15  aromatic radical or a C 7  -C 13  araliphatic radical, provided that R 3  is not methyl when R 1  and R 2  are each methyl, that R 3  is not ethyl when R 1  and R 2  are each methyl and that R 2  is not p-aminophenyl when R 1  is methyl and R 3  is ethyl with an organic compound having at least one group reactive with a P--H bond.

This application is a continuation of application Ser. No. 08/456,213, filed May 31, 1995, abandoned, which is a division of Ser. No. 08/203,961, filed Feb. 28, 1994, now U.S. Pat. No. 5,488,171, issued Jan. 30, 1996.

This invention relates to phosphinate esters, their preparation and their use in synthesis.

Phosphinate esters having a reactive P--H group and a protected P--H group have been used in the synthesis of pharmaceutically active substances such as the substituted propane-phosphonous compounds described in EP 0181833. In synthesis, the protected P--H group generally has be to converted into a P--H group after reaction of the protected phosphinate ester with another compound. With the known protected phosphinate esters previously used in such synthesis, the protecting group has had to be removed by hydrolysis under acid conditions. This imposes a limitation on the use of such protected phosphinate esters, since they cannot be used where hydrolysis under acid conditions would have an undesirable effect on other groups present.

It has now been found that certain phosphinates having a reactive P--H bond and a protected P--H bond, many of which are novel, can be reacted with compounds having at least one group reactive with a P--H bond to give products from which the protecting group can be removed by hydrolysis under mild basic conditions.

Accordingly, the present invention provides, in one aspect, a compound of formula ##STR2## where R¹ and R² are independently a C₁ -C₁₀ aliphatic radical, or R¹ is a C₁ -C₁₀ aliphatic radical and R² is a C₆ -C₁₀ aromatic radical, and R³ is a C₁ -C₈ aliphatic radical, a C₃ -C₈ cycloaliphatic radical, a C₆ -C₁₅ aromatic radical or a C₇ -C₁₃ araliphatic radical, provided that R³ is not methyl when R¹ and R² are each methyl, that R³ is not ethyl when R¹ and R² are each methyl and that R² is not p-aminophenyl when R¹ is methyl and R³ is ethyl.

Generally, in compounds of formula I as hereinbefore defined, R¹ and R² are independently C₁ -C₁₀ alkyl, which may be unsubstituted or substituted, for example by halogen, preferably fluorine or chlorine, or R¹ is such a group and R² is a C₆ -C₁₀ aryl group, which may be unsubstituted or substituted, for example by halogen.

R¹ or R² as unsubstituted or substituted C₁ -C₁₀ alkyl may be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl or n-decyl, or any of these groups substituted by halogen, for example 2-fluoroethyl, 2,2,2-trifluoroethyl, trichloromethyl, 2-chloroethyl, 2,2,2-trichloroethyl, or 2-chloro-n-propyl. R² as C₆ -C₁₀ aryl may be, for example, phenyl, o-tolyl, m-tolyl, p-tolyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl, alpha-naphthyl or beta-naphthyl. Preferably, R¹ and R² are independently C₁ -C₈ alkyl, or R¹ is C₁ -C₈ alkyl and R² is C₆ -C₈ aryl. In certain especially preferred compounds, R¹ and R² are each methyl, or R¹ is methyl and R² is n-hexyl, isobutyl or p-tolyl.

In formula I, R³ is generally C₁ -C₈ alkyl, which may be unsubstituted or substituted by, e.g., C₁ -C₄ alkoxy, C₁ -C₄ alkyl sulphonyl, cyano or halogen; C₃ -C₈ cycloalkyl, which may be unsubstituted or substituted e.g. by C₁ -C₄ alkoxy or halogen; C₆ -C₁₅ aryl, which may be unsubstituted or substituted e.g. by halogen, C₁ -C₄ alkoxy or nitro; or C₇ -C₁₃ aralkyl, which may be unsubstituted or substituted e.g. by C₁ -C₄ alkoxy or halogen.

R³ as unsubstituted or substituted C₁ -C₈ alkyl may be straight chain or branched, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, or any of these groups substituted by methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, methanesulphonyl, cyano, bromine, chlorine or fluorine such as methoxymethyl, 2-methoxyethyl, 2-ethoxymethyl, 2-n-butoxyethyl, 3-methoxypropyl, 1-methoxybutyl, 2-methoxybutyl, methanesulphonylmethyl, 2-methanesulphonylethyl, 2-cyanoethyl, 2-fluoroethyl, 2,2,2-trifluoroethyl, trichloromethyl, 2-chloroethyl,1-(chloromethyl) ethyl, 2,2,2-trichloroethyl, 2-chloro-n-propyl or 3-chloro-n-butyl.

R³ as unsubstituted or substituted C₃ -C₈ cycloalkyl may be, for example, cyclopropyl, cyclobutyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cycloheptyl or cyclooctyl, preferably cyclohexyl, or any of these groups substituted by methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, cyano, chlorine or fluorine.

R³ as unsubstituted or substituted C₆ -C₁₅ aryl may be, for example, phenyl, o-tolyl, m-tolyl, p-tolyl, o-xylyl, m-xylyl, p-xylyl, alpha-naphthyl or beta-naphthyl, or any of these groups substituted by halogen, C₁ -C₄ alkoxy or nitro. Preferably, R³ as C₆ -C₁₅ aryl is C₆ -C₈ aryl, especially phenyl.

R³ as unsubstituted or substituted C₇ -C₁₃ aralkyl may be, for example, benzyl, 4-methylbenzyl, o-methoxybenzyl, p-methoxybenzyl, diphenylmethyl, 2-phenylethyl, 2-phenylpropyl or 3-phenylpropyl, preferably C₇ -C₉ aralkyl, especially benzyl.

In one preferred class of compounds of formula I, R³ is C₁ -C₆ alkyl, which is unsubstituted or substituted by cyano, halogen or C₁ -C₄ alkoxy, especially methyl, ethyl, n-butyl, 2-cyanoethyl, 1-(chloromethyl) ethyl or 2-methoxyethyl. In another preferred class, R³ is branched alkyl, preferably C₂ -C₆ branched alkyl, especially isobutyl. In a further preferred class of compounds of formula I, R³ is C₅ to C₇ cycloalkyl or C₆ to C₈ aryl, especially cyclohexyl or phenyl.

In especially preferred classes of compounds of the invention, R¹ and R² are each methyl and R³ is ethyl, n-butyl or isobutyl; or R¹ is methyl, R² is isobutyl and R³ is 2-methoxyethyl,cyclohexyl or phenyl; or R¹ is methyl, R² is n-hexyl and R³ is 2-cyanoethyl; or R¹ is methyl, R² is p-tolyl and R³ is 1-(chloromethyl) ethyl.

Compounds of formula I may be prepared by esterifying a phosphonous (phosphinic) acid of formula ##STR3## with an alcohol of formula R³ OH, where R¹, R² and R³ are as hereinbefore defined.

The esterification reaction may be carried out at -10° to 40° C., preferably 0° to 20° C. It is conveniently effected in an organic solvent, for example a hydrocarbon such as toluene or, preferably, an ether such as diethyl ether, dioxan or, especially, tetrahydrofuran. The reaction is preferably carried out in the presence of a basic catalyst, usually a tertiary amine such as dimethylaminopyridine, and a dehydrating condensation agent such as N,N¹ -dicyclohexylcarbodiimide. A suitable procedure is described by Karanewsky and Badia, Tetrahedron Letters, 27,1751 (1986).

Compounds of formula I may be prepared by esterifying a phosphonous acid of formula II by reaction with a chloroformate of formula ClCOOR³ where R³ is as hereinbefore defined. This method can be useful where the chloroformate is commercially available, e.g. in the cases of methyl, ethyl, isopropyl, isobutyl, 2-bromoethyl, 2,2,2-chloroethyl, phenyl and benzyl chloroformates. It is conveniently carried out in an organic solvent in the presence of a base, preferably a tertiary amine such as triethylamine, using the procedure described by Hewitt, Aust. J. Chem. 32,463(1979). It may be effected at -20° to 40° C., preferably 0° to 20° C.

Phosphonous acids of formula II can be prepared by reaction of hypophosphorous acid (phosphinic acid) with a ketone of formula ##STR4## where R¹ and R² are as hereinbefore defined, in the presence of an acid catalyst, for example using an adaptation of the procedures described by C. Marie, C.r.134,288 and Ville J. Ann. Chim. Phys. 6! 23, 289 (1891). When R¹ and R² are both methyl, i.e. where the ketone is acetone, dimers form and the separation of the products is difficult. Where R¹ and R² are not both methyl, particularly where R¹ and R² are different, dimers are generally not formed.

Phosphonous acids of formula II can also be prepared by hydrolysis of an ester of formula ##STR5## where R¹ and R² are as hereinbefore defined and R⁴ is C₁ -C₄ alkyl, preferably methyl or ethyl. This hydrolysis can be effected by heating with water, acid or base.

Esters of formula IV can be prepared by reaction of hypophosphorous acid with a ketal of formula ##STR6## where R¹, R² and R⁴ are as hereinbefore defined, for example using the procedure described by S. J. Fitch, J. Amer. Chem. Soc. 86, 61 (1964).

Compounds of formula I can also be prepared by reaction of hypophosphorous acid with a ketal of formula ##STR7## where R¹, R² and R³ are as hereinbefore defined, for example using the procedure described in the abovementioned paper by S. J. Fitch.

Ketals of formula V or VI are either commerically available or may be prepared by known procedures. For example, where R¹ and R² are methyl, ketals of formulae V or VI where R⁴ or R³ respectively has at least 3 carbon atoms can be prepared from acetone dimethyl ketal by transketalisation using an alcohol of formula R⁴ OH or R³ OH in the presence of an acid as catalyst. A suitable procedure is described by Lorette and Howard, J. Org. Chem. 25,521 (1960).

Compounds of formula I can be prepared by reacting an alkyl phosphinate (hypophosphite) of formula ##STR8## with a ketone of formula III, where R³ is as hereinbefore defined, for example under the conditions described by S. J. Fitch, J. Amer. Chem. Soc. 86,61.(1964).

Compounds of formula I can also be prepared by reacting an alkyl hypophosphite of formula VII, generally at ambient temperature, with a silylating agent, preferably a dialkylhalosilane or trialkylhalosilane such as dimethylchlorosilane, trimethylchlorosilane or triethylchlorosilane, in the presence of a base, preferably a tertiary amine, to form a P(III) silyl compound which, where the silylating agent is a dialkylhalosilane or a trialkylhalosilane, is of formula VIII or VIIIA respectively ##STR9## where R⁵ is a C₁ -C₄ alkyl group, and reacting the P(III) silyl compound with a ketone of formula III, generally at a temperature of 30°-90° C., preferably 50° to 70° C.

Alkyl hypophosphites of formula VII can be prepared by reacting hypophosphorus acid with a corresponding alkyl orthocarboxylate, usually orthoformate, for example using the procedure described by S. J. Fitch, J. Amer. Chem. Soc. 86,61(1964), or by reacting hypophosphorous acid with a corresponding alkyl chloroformate in the presence of a base, usually a tertiary amine.

Compounds of formula I where R¹, R² and R³ are as hereinbefore defined, and compounds of formula I where the definitions of R¹, R² and R³ are not subject to the provisos hereinbefore stated, are useful in the synthesis of pharmaceutically active substances by reaction with compounds having at least one group reactive with a P--H bond. Accordingly, the present invention also provides use of a compound of formula ##STR10## where R¹ _(a) and R² _(a) are independently a C₁ -C₁₀ aliphatic radical, or R¹ _(a) is a C₁ -C₁₀ aliphatic radical and R² _(a) is a C₆ -C₁₀ aromatic radical, and R³ _(a) is a C₁ -C₈ aliphatic radical, a C₃ -C₈ cycloaliphatic radical, a C₆ -C₁₅ aromatic radical or a C₇ -C₁₃ araliphatic radical, for the synthesis of an organophosphorus compound by reaction of the compound of formula IA with an organic compound having at least one group reactive with a P--H bond.

R¹ _(a), R² _(a) and R³ _(a) may be chosen from the same groups as R¹, R² and R³ respectively, free from the provisos hereinbefore stated with respect to the definitions of R¹, R² and R³ in formula I, i.e. R¹ _(a), R² _(a) and R³ _(a) can each be methyl, R¹ _(a) and R² _(a) can each be methyl when R³ _(a) is ethyl and R² _(a) can be p-aminophenyl when R¹ is methyl and R³ is ethyl.

Compounds of formula IA which are also compounds of formula I can be prepared as hereinbefore described. Compounds of formula IA where R¹ _(a), R² _(a) and R³ _(a) are each methyl can be prepared as described by S. J. Fitch, J. Amer. Chem. Soc. 86,61 (1964). Compounds of formula IA where R¹ and R² are methyl and R³ is ethyl can be prepared as described by C. Marie, A. ch. 8!, 3, 370.

In synthetic procedures, the reaction product of the compound of formula IA and the compound having a group reactive with P--H, or derivatives of this reaction product in which the protecting HO--C(R¹ _(a))R² _(a) -- group derived from the compound of formula IA is retained, may be reacted with a hydrolysing agent to remove this protecting group and generate a P--H bond when desired. It has surprisingly been found that such deprotection can be effected by hydrolysis with a base, usually by heating with aqueous ammonia at temperatures from ambient to 100° C., preferably 70°-90° C.

The compound having one or more groups reactive with a P--H bond may be, for example, a compound having at least one aldehyde or ketone group or a compound having at least one ethylenic double bond. Sugars having such reactive groups are particularly useful in the synthesis of compounds having antiviral activity. In accordance with the invention, the compound having at least one group reactive with a P--H bond is preferably a compound having an ethylenic double bond, especially a sugar having such a double bond.

In one particularly useful synthesis, for example, a compound of formula I is reacted, in the presence of a free radical initiator, with an olefinic sugar acetonide of formula ##STR11## where R⁶ is hydrogen, substituted or unsubstituted C₁ -C₁₀ alkyl, C₂ -C₁₀ alkenyl, C₆ -C₁₅ aryl or C₇ -C₁₆ aralkyl, R⁷ CO-- where R⁷ is substituted or unsubstituted C₁ -C₁₀ alkyl, C₂ -C₁₀ alkenyl, C₃ -C₈ cycloalkyl, C₆ -C₁₅ aryl or C₇ -C₁₆ aralkyl, or R⁵ is silyl substituted by three C₁ -C₁₅ hydrocarbyl groups, to give a compound of formula ##STR12## where R¹, R², R³ and R⁶ are as hereinbefore defined.

Suitable initiators include azo compounds such as azobis(isobutyronitrile), peroxides such as benzoyl peroxide, tert-butyl peroxide or 2,2-bis(tert-butylperoxy)propane, peresters such as tert-butyl perbenzoate or tert-butyl per-2-ethylhexanoate, percarbonates such as diacetyl perdicarbonate or bis(4-tert-butylcyclohexyl)perdicarbonate or persalts such as potassium persulphate. The initiator is generally used in an amount of 0.1 to 100 mol. %, preferably 5 to 15 mol %, per mol of the olefinic compound of formula IX. The reaction may be carried out without a solvent, but is preferably carried out in an organic solvent, usually an aromatic hydrocarbon such as benzene, toluene or xylene. It may be carried out at temperatures of 30° to 100° C., preferably 70° to 90° C.

Compounds of formula X may be converted, by reaction with a hydrolysing agent for the acetonide group, for example an acidic ion exchange resin, followed by esterification with an acid of formula R⁸ COOH or an anhydride or acyl halide thereof, into compounds of formula ##STR13## where R⁸ is substituted or unsubstituted C₁ -C₁₀ alkyl, C₂ -C₁₀ alkenyl, C₃ -C₈ cycloalkyl, C₆ -C₁₅ aryl or C₇ -C₁₆ aralkyl and R¹, R², R³ and R⁶ are as hereinbefore defined.

Compounds of formula XI may be converted, by glycosylation with nucleoside bases such as thymine, into nucleotide analogues of formula ##STR14## where B is a nucleoside base radical such as thyminyl, and R¹, R², R³, R⁶ and R⁸ are as hereinbefore defined.

This reaction may be carried out using known glycosylation procedures, for example in the presence of a silylating agent such as trimethylsilyl chloride, bis(trimethylsilyl)acetamide or hexamethyldisilazane and a catalyst such as a fluoralkanesulphonate salt in an organic solvent such as acetonitrile or 1,2-dichloroethane at a temperature of 40°-90° C. followed by treatment with an aqueous acid, usually an organic acid such as acetic acid, to regenerate the tertiary hydroxyl group which has become silylated during the glycosylation reaction.

Compounds of formula XII where R⁶ is R⁷ CO-- can be converted, by basic hydrolysis of the R⁷ COO-- and R⁸ COO-- groups using, for example, potassium carbonate in methanol, followed by removal of the P--H protecting group by hydrolysis with aqueous ammonia, suitably at 70°-90° C., followed by acidification, into nucleotide analogues of formula ##STR15## where R³ and B are as hereinbefore defined.

Compounds of formula XIII can be reacted, through the deprotected P--H bond, after suitable protection of the OH groups, with nucleotide analogues having an aldehyde group or ethylenic double bond to give dinucleotide analogues having antiviral properties.

Olefinic sugar acetonides of formula IX can be prepared by reaction of 1,2,5,6-di-O-isopropylidene-α-D-allofuranose (prepared as described in Carbohyd. Res. 24 (1972) 192) with a compound of formula R⁶ _(a) X or (R⁶ _(a) CO)₂ O where R⁶ _(a) is the same as R⁶ except that R⁶ _(a) cannot be hydrogen and X is a halogen atom or a hydroxyl group, to etherify or esterify the hydroxyl group on the furanose ring, reacting the product with 80% acetic acid at ambient temperature to hydrolyse the acetonide group, reacting the hydrolysis product with methanesulphonyl chloride in the presence of a base to replace both hydroxyl groups by methane sulphonyloxy groups, and reacting the dimethanesulphonyloxy product with sodium iodide in methyl ethyl ketone at 70°-90° C., to give an acetonide of formula IX in which R⁶ is R⁶ _(a), which can be hydrolysed by treatment with potassium carbonate in aqueous methanol at ambient temperature to give an acetonide of formula IX in which R⁶ is hydrogen.

The invention is illustrated by the following Examples.

EXAMPLE 1

Commercial hypophosphorous acid (50%) is concentrated to 94% on a rotary evaporator. A mixture of hypophosphorous acid (94%, 210.6 g, 3M) and 2,2-dimethoxypropane (917 g, 8.8M) is allowed to stand at room temperature for 6 days. The mixture is evaporated under vacuum and distilled on a wiped-wall still to give methyl(1-hydroxy-1-methylethyl)phosphinate (268 g, 65%, b.p. 65° C./0.1 mm). ³¹ P nmr (CDCl₃, 24.15 MHz)δ=45 ppm, J_(PH) 545 Hz. (Fitch J. Amer. Chem. Soc. 1964, 86, 61).

The methyl (1-hydroxy-1-methylethyl)phosphinate prepared as described immediately above is heated with water (1 l) on a steam bath for 8 hours until conversion to 1-hydroxy-1-methylethylphosphonous acid is complete (monitored by ³¹ P nmr). The water is removed on a rotary evaporator and the residue is completely dried by co-evaporation with toluene. A sample of this phosphonous acid (4.6 g, 0.037M), isobutyl alcohol (3.02 g, 0.041M) and dimethylaminopyridine (0.5 g, 0.0041M) is stirred at 5° C. in tetrahydrofuran. Dicyclohexylcarbodiimide (8.4 g, 0.041M) is added portionwise over 30 minutes. On completion of the reaction (³¹ P nmr), ether (50 ml) is added and the precipitated dicyclohexyl urea is filtered off. Evaporation of the ether liquors gives a pale yellow oil (6.7 g) which is purified by chromatography on silica using ether, then ethyl acetate, as eluant to give isobutyl(1-hydroxy-1-methylethyl)phosphinate.

Found: C 47.0, H 9.5, P 17.1%; C₇ H₁₇ O₃ P requires C 46.7, H 9.5, P 17.2%.

³¹ P nmr (CDCl₃, 162 MHz)δ=42.2 ppm.

EXAMPLE 2

2,2-Diethoxypropane (3.96 g, 0.03M) and hypophosphorous acid (100%, 0.66 g, 0.01M) are allowed to stand at room temperature for 5 days. The mixture is distilled on a wiped-wall still to give ethyl(1-hydroxy-1-methylethyl)phosphinate, (b.p. 70°/0.3 mm).

³¹ P nmr (CDCl₃, 36.21 MHz)δ=41.6 ppm.

Found: C 39.4, H 8.6, P 20.4%; C₅ H₁₃ O₃ P requires C 39.5, H 8.6, P 20.8%.

EXAMPLE 3

Hypophosphorous acid (100%, 2.0 g, 0.03M) and ethyl chloroformate (3.3 g, 0.03M) are stirred under nitrogen at room temperature in THF (40 ml). Triethylamine (3.03 g, 0.03M) is carefully added with cooling over 1 hour. ³¹ P nmr shows that there is 85% conversion to ethyl hypophosphite (³¹ P nmrδ=16 ppm). Trimethylsilyl chloride (3.3 g, 0.3M) is added followed by triethylamine (3.03 g, 0.03M). The mixture is stirred for 1 hour, when conversion to ethyltrimethylsilyl phosphinate (³¹ P nmrδ=149 ppm) is complete. Acetone (5 ml) is added and the mixture is stirred for 1 hour at 60° C. The mixture is then cooled, quenched with water and washed with methylene chloride. The aqueous phase is evaporated and the residual gum is stirred with ether. Evaporation of the ether gives ethyl (1-hydroxy-1-methylethyl)phosphinate after distillation.

EXAMPLE 4

A mixture of 2,2-dimethoxypropane (31.2 g, 0.3M), n-butanol (48.9 g, 0.66M) and toluene-p-sulphonic acid (0.05 g) is heated at 110° C., removing a fraction boiling below 60° C. over 2 hours. The mixture is cooled, brought to pH 9 with sodium methoxide in methanol, then distilled to give acetone di-n-butylketal b.p. 80° C./15 mm Hg, (33.8 g 60%). A sample of this ketal (18.8 g 0.1 m) and hypophosphorous acid (2.2 g, 0.033M) are stirred at room temperature for 7 days. Fractional distillation gives n-butyl (1-hydroxy-1-methylethyl)phosphinate (b.p. 84° C./0.3 mm Hg).

³¹ P nmr (CDCl₃ 36.21 MHz)δ=44.4 ppm.

EXAMPLE 5

1-hydroxy-1-methylethylphosphonous acid, prepared as described in Example 1, (9.92 g, 0.08M) is dissolved in dichloromethane (100 ml) at 0° C. and isobutyl chloroformate (21.85 g, 0.16M) is added in one portion. Triethylamine (16.19 g, 0.16M) is added dropwise over 1 hour maintaining the temperature at 0° C. The mixture is allowed to warm to room temperature, the precipitated solid is filtered off and the filtrate is evaporated to an oil. This oil is distilled on a wiped-wall still to give isobutyl(1-hydroxy-1-methylethyl)phosphinate (b.p. 76°-8° C./0.1 mm Hg)

³¹ P nmr (CDCl₃, 162 MHz)δ=42.2 ppm, J_(PH) =532.8 Hz.

EXAMPLE 6

A mixture of octan-2-one (3.76 g, 0.29M) and hypophosphorus acid (91.5%, 2.09 g, 0.029M) is heated at 100° C. for 12 hours in the presence of Dowex 50W×2 ion exchange resin (1 ml, aqueous slurry). The mixture is cooled to room temperature, methanol (50 ml) is added and the Dowex is removed by filtration. The filtrate is evaporated to an oily residue, which is dissolved in ethyl acetate, washed with water, brine, then dried (MgSO₄). Removal of the solvent gives 1-hydroxy-1-methylheptylphosphonous acid.

³¹ P NMR (CDCl₃, 162 MHz)δ=39 ppm. J._(PH) =545 Hz.

3.88 g (0.02M) of the 1-hydroxy-1-methylheptylphosphonous acid, 3-hydroxypropionitrile (1.42 g, 0.02M) and dimethylaminopyridine (0.122 g, 0.001M) are stirred in tetrahydrofuran (75 ml) under argon at room temperature. Dicyclohexylcarbodiimide (4.54 g, 0.022M) is added and the mixture is stirred for 1 hour. On completion of the reaction (³¹ P NMR, TLC), ether (150 ml) is added and the precipitated dicyclohexyl urea is filtered off. Evaporation of the ether liquors gives a pale yellow oil (4.9 g) which is purified by chromatography on silica using ethyl acetate as eluant to give 2-cyanoethyl (1-hydroxy-1-methylheptyl)phosphinate.

³¹ P NMR (CDCl₃, 162 MHz)δ=42.9, 43.69 ppm J_(PH) =540 Hz.

EXAMPLE 7

A mixture of p-methylacetophenone (2.68 g. 0.02M) and hypophosphorous acid (90%, 1.45 g. 0.02M) is heated on a steam bath for 12 hours. The reaction mixture is poured into ice-water and the organic material is extracted with ethyl acetate. Evaporation and co-evaporation with toluene gives a white solid which is crystallised from chloroform/hexane. There is obtained 1-hydroxy-1-p-tolylethylphosphonous acid, m.p. 115° C.

³¹ P NMR (CDCl₃, 162 MHz)δ=38.4 ppm J_(PH) =540 Hz.

1-hydroxy-1-p-tolylethylphosphonous acid (0.2 g., 0.01M), 1-chloro-2-propanol (0.094 g., 0.01M) and dimethylaminopyridine (0.01 g) are stirred in tetrahydrofuran (5 ml.) at 5° C. Dicyclohexylcarbodiimide (0.23 g., 0.001M) is added portionwise over 1 hour. On completion of the reaction (monitored by ³¹ P NMR) ether (10 ml) is added and the dicylohexylurea formed is filtered off. Evaporation of the filtrate gives an oil which is purified by chromatography on silica using 5% methanol in chloroform as eluant. There is obtained 1-chloromethylethyl (1-hydroxy-1-p-tolylethyl) phosphinate.

³¹ P NMR (CDCl₃ 162 MHz)δ=41.5, 41.4, 40.5, 39.5 ppm.

EXAMPLE 8

A mixture of methyl isobutyl ketone (3.0 g 0.03M) and hypophosphorous acid (90%, 1.45 g., 0.02M) is heated on a steam bath for 8 hours. The resulting mixture is poured into water and the organic material is extracted into ethyl acetate and washed with water until no more hypophosphorous acid remains (³¹ P NMR). The solvent and excess of ketone are removed under vacuum and the residual oil is purified by chromatography on silica using 10% methanol in chloroform. There is obtained 1-hydroxy-1,4-dimethylbutylphosphonous acid.

³¹ P NMR (CDCl₃, 162 MHz)δ=39.4 ppm J_(PH) =550 Hz.

1-Hydroxy-1,4-dimethylbutylphosphonous acid (0.166 g., 0.001M), phenol (0.094 g., 0.001M) and dimethylaminopyridine 0.01 g.) are stirred in tetrahydrofuran (5 ml.) at 5° C. Dicyclohexylcarbodiimide (0.23 g. 0.001M) is added portionwise over 2 hours. On completion of the reaction (³¹ P NMR) ether (10 ml.) is added and the dicylohexyl urea formed is filtered off. Evaporation of the filtrate gives an oil which is purified on silica using 5% methanol in chloroform as eluant. There is obtained phenyl (1-hydroxy-1,4-dimethylbutyl)phosphinate.

³¹ P NMR (CDCl₃, 162 MHz)δ=41.36, 41.21, 40.87, 40.72 ppm J_(PH) =550 Hz.

EXAMPLE 9

1-Hydroxy-1,4-dimethylbutylphosphonous acid (0.166 g., 0.001M), cyclohexanol (0.1 g., 0.001M) and dimethylaminopyridine (0.01 g.) are stirred in tetrahydrofuran (10 ml.) at 5° C. Dicyclohexylcarbodiimide (0.23 g., 0.001M) is added portionwise over 4 hours. On completion of the reaction (³¹ P NMR) ether (10 ml) is added and the dicyclohexylurea formed is filtered off. The filtrate is evaporated, then co-evaporated with methanol, to give a waxy solid which is purified on silica using 5% methanol in chloroform as eluant.

There is obtained cyclohexyl (1-hydroxy-1,4-dimethylbutyl) phosphinate.

³¹ P NMR (CDCl₃, 162 MHz)δ=38.7, 39.3, 39.9 ppm J_(PH) 540 Hz.

EXAMPLE 10

1-Hydroxy-1,4-dimethylbutylphosphonous acid prepared as described in Example 8 (0.166 g. 0.001M), 2-methoxyethanol (0.076 g. 0.001M) and dimethylaminopyridine (0.01 g.) are stirred in THF (5 ml.) at 5° C. Dicyclohexylcarbodiimide (0.23 g., 0.001M) is added portionwise and the mixture is stirred for 3 hours. Ether (10 ml.) is added and the dicyclohexylurea is filtered off. The filtrate is evaporated and the residue is dissolved in chloroform and washed with water. Evaporation of the chloroform gives an oil which is purified on silica using ethyl acetate as eluant. There is obtained 2-methoxyethyl (1-hydroxy-1,4-dimethylbutyl)phosphinate.

³¹ P NMR (CDCl₃, 162 MHz)δ=44.9, 44.5 ppm J_(PH) =540 Hz.

EXAMPLES 11-16

These Examples illustrate the use of compounds of formula I in synthesis, the initial reaction being between a compound of formula I and Compound A, which is an olefinic sugar acetonide of formula IX where R⁶ is hydrogen, prepared as hereinbefore described from 1,2,5,6-di-O-isopropylidene-α-D-allofuranose.

EXAMPLE 11

This Example describes the preparation of the compound of formula ##STR16##

A solution of isobutyl (1-hydroxy-1-methylethyl) phosphinate (7.22 g, 0.0403M) and t-butylcyclohexylperdicarbonate (0.5 g) in toluene (1 ml) is heated to 80° C. and stirred under argon. A solution of Compound A and t-butyl cyclohexylperdicarbonate (2 g) in toluene (4 ml) is added slowly over 30 minutes and the mixture is stirred for 4 hours. When reaction is complete (monitored by ³¹ P nmr) the solvent is evaporated in vacuo to give a pale yellow oil. The oil is chromatographed on silica using ether, ethyl acetate and finally 5% methanol in ethyl acetate gradient as chants. There is obtained Compound B as an oil which partly solidifies. Found C 52.7, H 8.5, P 8.7; C₁₆ H₃₀ O₇ P requires C 52.6, H 8.3 P 8.5%. ³¹ P nmr (CDCl₃, 162 MHz): δ 56.85, 57.2 ppm.

EXAMPLE 12

This Example describes the preparation of the compound of formula ##STR17##

To Compound B (8.25 g, 0.0226M) in dimethoxyethane (200 ml) is added a slurry (50 ml) of Dowex 50W×2 (100), H⁺ form, in water and the mixture is heated to 80° C. for 12 hours then cooled. The Dowex is removed by filtration to give a pale yellow solution. Evaporation of the solvent gives Compound C as an oil which is not purified further. ³¹ P nmr (CD₃ OD, 162 MHz):δ=63.2, 63.4, 64.3 and 64.4 ppm.

EXAMPLE 13

This Example describes the preparation of the compound of formula ##STR18##

Compound C (20 g, 0.0613M) is added to a mixture of pyridine (40 ml) and acetic anhydride (40 ml) with cooling, maintaining the temperature below 30° C. Reaction is complete in 20 minutes (Monitored by TLC). The excess of acetic anhydride and pyridine are removed by evaporation. The residual oil is dissolved in chloroform and washed with dilute hydrochloric acid, sodium bicarbonate and brine and dried over MgSO₄. Evaporation gives a yellow syrup which is purified by chromatography with silica. There is obtained Compound D. Found C 50.4; H 7.15, P 6.65; C₁₉ H₃₂ O₁₀ P requires C 50.55, H 7.15, P 6.9%. ³¹ P nmr (CDCl₃, 162 MHz):δ55.5, 55.7, 55.8 ppm.

EXAMPLE 14

This Example describes the preparation of the compound of formula ##STR19##

A mixture of thymine (6.31 g, 0.05M), N, O-bis trimethylsilyl acetamide (20.34 g, 0.1M) and dichloroethane (125 ml) is heated to 80° C. under argon until a clear solution is obtained. The solution is cooled to room temperature and a solution of Compound D (22.57 g, 0.05M) in dichloroethane (75 ml) is added followed by trimethylsilyltrifluoromethane sulphonate (32.91 g, 0.125M). The reaction mixture is heated to 50° C. and stirred for 8 hours until reaction is complete (TLC). Chloroform (300 ml) and water (200 ml) are added followed by saturated sodium bicarbonate solution until the aqueous phase is neutral. The mixture is washed with chloroform (3×100 ml) and the extracts are washed with water then brine and dried (MgSO₄). Evaporation gives a viscous liquid which is chromatographed on silica using 5% methanol in chloroform as eluant. There is obtained a colourless oil which is dissolved in acetic acid, water and tetrahydrofuran (100 ml 3:1:1 ratio) and heated on a steam bath for 15 minutes. The solvent is removed by evaporation followed by co-evaporation with methanol then chloroform. There is obtained Compound E as a white hygroscopic solid.

Found C 50.9, H 6.9, N 5.2, P 5.9; C₂₂ H₃₅ O₁₀ N₂ P requires C 50.95, H 6.8, N 5.4, P 5.9%. ³¹ P nmr (CDCl₃, 162 MHz): δ 56.0, 56.3 ppm.

EXAMPLE 15

This Example describes the preparation of the compound of formula ##STR20##

Compound E (4.4 g, 0.0085M) dissolved in methanol (5 ml) is added to potassium carbonate (2.34 g, 0.017M) in water (5 ml) and the mixture is stirred for 15 minutes. The mixture is evaporated to dryness and the residue is stirred with acetone. The inorganic solids are removed by filtration and the acetone is evaporated to give Compound F as an oil. ³¹ P nmr (D₂ O, 162 MHz):δ=63.0 ppm.

EXAMPLE 16

This Example describes the preparation of a compound of formula ##STR21##

Compound F (3.7 g) is dissolved in 10% aqueous ammonia and heated up to 80° C. for 12 hours. The mixture is cooled and evaporated to an oil which is purified on ion exchange resin Dowex 50W×2 (100) acid form using water as eluant. There is obtained Compound G as a white foamy solid which is lyophilised to a white hygroscopic solid.

Found: C 40.9, H 5.3, N 8.3, P 9.4%; C₁₁ H₁₇ N₂ O₇ P requires C 41.25, H 5.35, N 8.75, P 9.7%.

³¹ P nmr (D₂ O, 162 MHz): δ 36.3 ppm, J_(PH) =540 Hz. 

What is claimed is:
 1. A method of synthesis of an organophosphorus compound, which comprises reacting a compound of the formula ##STR22## where R¹ _(a) and R² _(a) are independently a C₁ -C₁₀ aliphatic radical, or R¹ _(a) is a C₁ -C₁₀ aliphatic radical and R² _(a) is a C₆ -C₁₀ aromatic radical, and R³ _(a) is a C₁ -C₈ aliphatic radical, a C₃ -C₈ cycloaliphatic radical, a C₆ -C₁₅ aromatic radical or a C₇ -C₁₃ araliphatic radical, with an organic compound having at least one group reactive with a P--H bond.
 2. A method according to claim 1, which comprises reacting a compound of the formula ##STR23## where R¹ and R² are independently a C₁ -C₁₀ aliphatic radical, or R¹ is C₁ -C₁₀ alkyl or halogen-substituted C₁ -C₁₀ alkyl and R² is a C₆ -C₁₀ aromatic radical, and R³ is a C₁ -C₈ aliphatic radical, a C₃ -C₈ cycloaliphatic radical, a C₆ -C₁₅ aromatic radical or a C₇ -C₁₃ araliphatic radical, provided that R³ is not methyl when R¹ and R² are each methyl, that R³ is not ethyl when R¹ and R² are each methyl, and that R² is not p-aminophenyl when R¹ is methyl and R³ is ethyl, with an organic compound having at least one group reactive with a P--H bond.
 3. A method according to claim 1, in which R¹ _(a) and R² _(a) are independently unsubstituted or halogen-substituted C₁ -C₁₀ alkyl, or R¹ is unsubstituted or halogen-substituted C₁ -C₁₀ alkyl and R² is unsubstituted or substituted C₆ -C₁₀ aryl, and R³ _(a) is C₁ -C₈ alkyl which is unsubstituted or substituted by C₁ -C₄ alkoxy, C₁ -C₄ alkyl sulphonyl, cyano or halogen; C₃ -C₈ cycloalkyl which is unsubstituted or substituted by C₁ -C₄ alkoxy or halogen; C₆ -C₁₅ aryl which is unsubstituted or substituted by halogen, C₁ -C₄ alkoxy or nitro; or C₇ -C₁₃ aralkyl which is unsubstituted or substituted by C₁ -C₄ alkoxy or halogen.
 4. A method according to claim 3, in which R¹ _(a) and R² _(a) are each methyl, or R¹ _(a) is methyl and R² _(a) is n-hexyl,isobutyl or p-tolyl, and R³ _(a) is methyl, ethyl, n-butyl, 2-cyanoethyl, 1-(chloromethyl) ethyl, 2-methoxyethyl, isobutyl, cyclohexyl or phenyl.
 5. A method according to claim 1, in which the reactive group is an aldehyde or ketone group or an ethylenic double bond.
 6. A method according to claim 1, in which the compound having the reactive group is a sugar having an ethylenic double bond.
 7. A method according to claim 1, in which the product of said reaction, or a derivative thereof in which a protecting HO--C(R¹ _(a))R² _(a) -- group is retained, is reacted with a hydrolysing agent to remove said protecting group.
 8. A method according to claim 7, in which said hydrolysing agent is a base.
 9. A method acccording to claim 8, in which the base is aqueous ammonia.
 10. A method according to claim 2, in which R¹ and R² are independently unsubstituted or substituted C₁ -C₁₀ alkyl, or R¹ is unsubstituted or substituted C₁ -C₁₀ alkyl and R² is unsubstituted or substituted C₆ -C₁₀ aryl.
 11. A method according to claim 2, in which R¹ and R² are independently C₁ -C₈ alkyl, or R¹ is C₁ -C₈ alkyl and R² is C₆ -C₈ aryl.
 12. A compound according to claim 2, in which R¹ and R² are each methyl or R¹ is methyl and R² is n-hexyl, isobutyl or p-tolyl.
 13. A method according to claim 2, in which R³ is unsubstituted or substituted C₁ -C₈ alkyl, C₃ -C₈ cycloalkyl, C₆ -C₁₅ aryl or C₇ -C₁₃ aralkyl.
 14. A method according to claim 2, in which R³ is C₁ -C₆ alkyl which is unsubstituted or substituted by cyano, halogen or C₁ -C₄ alkoxy, or R³ is C₅ to C₇ cycloalkyl or C₆ to C₈ aryl.
 15. A method according to claim 2, in which R³ is branched C₂ -C₆ alkyl. 